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A transverse kick resulting from the coaxial rf coupler in the L-band rf gun at the photoinjector test facility at DESY in Zeuthen (PITZ) has been systematically studied in simulations and further characterized in experiments. The used rf macro-pulse for the gun is typically 600 μs long and applied to produce a train of up to 2700 electron bunches. The kick is transient and found to be dependent on the detuning of the resonance frequency of the gun cavity. The frequency detuning within the rf pulse results in a variation in the kick strength along the pulse. This leads to a downstream orbit and size change of individual bunches within the train. Using 3D rf field distributions, calculated at resonant and detuned frequencies of the cavity, particle tracking simulations are performed to evaluate the integral kick location and strength, simulate its transient behaviors with respect to gun launch phase and detuned frequency of the gun cavity, and thereby emulate its impacts onto the electron bunch. In the experiments, the temperature of the cooling water for the gun is tuned, allowing detailed characterization of the frequency detuning within the rf pulse and thus measurements of the kick which are of practical interest for machine operation. The resulting orbit and size change along a 240 μs bunch train have been measured downstream at the injector exit for an rf gun peak power of about 5.7 MW. A measured focusing difference between head and tail of the bunch train is evaluated in terms of the gun solenoid current which provides more relevant information for overall tuning of the FELs. This is exemplarily given for both the under- and over-focusing case. The obtained results will be presented and discussed.

4th European Advanced Accelerator Concepts Workshop, EAAC2019, La Biodola, Italy, 15 Sep 2019 - 21 Sep 2019; Journal of physics / Conference Series 1596(1), 012003 (2020). doi:10.1088/1742-6596/1596/1/012003, Beam-driven plasma wakefield acceleration (PWFA) allows for high gradient acceleration of electron beams and hence is a promising candidate for compact and cost-efficient drivers of applications demanding high brightness beams. One of the main challenges in these accelerators is to control beam-plasma instabilities with rapid growth rates which are induced by the strong transverse components of the wakefields. The hosing instability, a growing transverse oscillation of the beam centroid caused by coherent coupling between bunch slice centroids and transverse wakefields, was predicted to set severe limits on the possible acceleration distance in PWFAs. Several methods have been proposed to damp or even suppress the hosing of the beam, prevent beam-breakup and thus allow stable operation. Here, we present preparations and simulation studies aiming at the experimental investigation of hosing suppression mechanisms at the PITZ facility., Published by IOP Publ., Bristol

Physical review letters 122(4), 044801 (2019). doi:10.1103/PhysRevLett.122.044801, Temporally modulated electron beams have a wide array of applications ranging from the generation of coherently enhanced electromagnetic radiation to the resonant excitation of electromagnetic wakefields in advanced-accelerator concepts. Likewise producing low-energy ultrashort microbunches could be useful for ultrafast electron diffraction and new accelerator-based light-source concepts. In this Letter we propose and experimentally demonstrate a passive microbunching technique capable of forming a picosecond bunch train at ∼6 MeV. The method relies on the excitation of electromagnetic wakefields as the beam propagates through a dielectric-lined waveguide. Owing to the nonultrarelativistic nature of the beam, the induced energy modulation eventually converts into a density modulation as the beam travels in a following free-space drift. The modulated beam is further accelerated to ∼20 MeV while preserving the imparted density modulation., Published by APS, College Park, Md.

10th International Particle Accelerator Conference, IPAC'19, Melbourne, Australia, 19 May 2019 - 24 May 2019; Journal of physics / Conference series Conference series [...] 1350, 012036 - (2019). doi:10.1088/1742-6596/1350/1/012036, A free-electron laser based THz source is undergoing design studies at the Photo Injector Test facility at DESY in Zeuthen (PITZ). It is considered as a prototype for pump-probe experiments at the European XFEL, benefiting from the fact that the electron beam from the PITZ facility has an identical pulse train structure as the XFEL pulses. In the proposed proof-of-principle experiment, the electron beam (up to 4 nC bunch charge and 200 A peak current) will be accelerated to 16-22 MeV/c to generate SASE radiations in an LCLS-I undulator in the THz range between 60 and 100 pm with an expected energy of up to ~1 mJ/pulse. In this paper, we report our simulations on the optimization of the photo-injector and the design of the transport and matching beamline. Experimental investigations on the generation, characterization and matching of the high charge beam in the existing 22-m-long beamline will also be presented., Published by IOP Publ.20382, Bristol

10th International Particle Accelerator Conference, IPAC’19, Melbourne, Australia, 2 May 2019 - 24 May 2019; Journal of physics / Conference series Conference series [...] 1350, 012046 - (2019). doi:10.1088/1742-6596/1350/1/012046, Laser pulse shaping is one of the key elements to generate low emittance electron beams with RF photoinjectors. Ultimately high performance can be achieved with ellipsoidal laser pulses, but 3-dimensional shaping is challenging. High beam quality can also be reached by simple transverse pulse shaping, which has demonstrated improved beam emittance compared to a transversely uniform laser in the 'pancake' photoemission regime. In this contribution we present the truncation of a Gaussian laser at a radius of approximately one sigma in the intermediate (electron bunch length directly after emission about the same as radius) photoemission regime with high acceleration gradients (up to 60 MV/m). This type of electron bunch is used e.g. at the European XFEL and FLASH free electron lasers at DESY, Hamburg site and is being investigated in detail at the Photoinjector Test facility at DESY in Zeuthen (PITZ). Here we present ray-tracing simulations and experimental data of a laser beamline upgrade enabling variable transverse truncation. Initial projected emittance measurements taken with help of this setup are shown, as well as supporting beam dynamics simulations. Additional simulations show the potential for substantial reduction of slice emittance at PITZ., Published by IOP Publ.20382, Bristol

44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) : [Proceedings] - IEEE, 2019. - ISBN 978-1-5386-8285-2 - doi:10.1109/IRMMW-THz.2019.8874425 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2019, Paris, France, 1 Sep 2019 - 6 Sep 2019; IEEE 1 pp. (2019). doi:10.1109/IRMMW-THz.2019.8874425, There is a high demand for intense THz sources since “many excitation mechanisms of matter resonate in the terahertz regime” especially for condensed matters. “Accelerator-based THz sources provide the wide tunability together with high intensity and repetition rates beyond 100 kHz, that will enable broad application at the European XFEL to the most interesting scientific problems in the field” [1]. Supported by European XFEL a proof of principle study is started at the Photo-Injector Test Facility located at DESY in Zeuthen site (PITZ). Since PITZ and European XFEL electron sources are identical the X-ray and THz radiation can be produced with identical bunch train structure so that for every X-ray pulse a corresponding THz pulse can be provided for the pump-and- probe experiments., Published by IEEE

3rd European Advanced Accelerator Concepts workshop, EAAC 2017, Elba, Italy, 24 Sep 2017 - 30 Sep 2017; Nuclear instruments & methods in physics research / A 909, 107 - 110 (2018). doi:10.1016/j.nima.2018.02.043, Beam driven plasma acceleration is one of the most promising candidates for future compact particle accelerator technologies. In this scheme a particle bunch drives a wake in a plasma medium. The fields inside of the wake can be used to accelerate a trailing witness bunch. To maximise the ratio between acceleration of the witness to deceleration of the drive bunch, the so called transformer ratio, several methods have been proposed. The ones yielding the most favorable results are based on shaped drive bunches that are long in terms of the plasma wavelength. We present here methods to create such drive bunches employing temporally shaped UV-laser pulses for the extraction of electron bunches from a photo-electron gun. Theoretical considerations, experimental results and possibilities for further improvements are discussed., Published by North-Holland Publ. Co., Amsterdam

Summary form only given. The Spherical Theta Pinch was developed at the Institute for Applied Physics at the Goethe University Frankfurt. It consists of a spherical coil with less than 10 windings which are arranged around a glass vessel with a volume of several liters. A capacitor bank is discharged trough a self-developed thyristor stack. The rising current in the coil ionizes the gas inside the glas vessel and the magnetic fields compress the plasma on the symmetry axis. Due to the spherical assembly the pinch is more stable than in common linear theta pinch machines.1 The capacitors and the coil form a LCR-circuit with a resonance frequency of around 10kHz, the stored energy in the capacitors reaches 5kJ at a voltage of 15kV and the maximum currents are 8kA.After the development of several prototypes and intense e,amination, the first theta pinch device was now tested as a plasma stripper at the GSI facility, Darmstadt. For reaching higher charge states of ions, which minimize the acceleration distance, stripping foils are used at the moment. As these foils bear several mechanical and technical problems and furthermore only allow a small increment of the charge state, stripping plasmas have been proposed as an alternative. Compared to formerly used Z-pinches the theta pinch has the advantage of almost unlimited lifetime, as no electrodes are in contact with the plasma discharge and could thus erode. Other applications which are investigated are the generation of intense VUV-pulses and the use as a pulsed high current H+ ion source.